1. Field of the Invention
The present invention relates to an arrangement of a color enlarger head having a diffusion box including a scattering type light diffusion means to equalize respective colored light rays emitted from a light source and, more particularly, to an arrangement of a light distribution adjusting box for irradiation of an original picture negative with said light rays.
2. Description of the Related Art
A color enlarger generally includes a light source, a head, a carrier, an enlarging lens, and a table. Referring to FIG. 5 of the accompanying drawings, light rays emitted from a source lamp 2 provided in a light source 1, are transmitted through filters 4 having appropriate color characteristics, thereby respectively coloring the light rays. The light rays then enter a diffusion box 8, which is part of the head 6, through an entrance window 8a. Diffusion box 8 has an inner surface made up of a diffuse reflector. The respectively colored light rays are diffusively reflected on the diffuse reflector in order to equalize the light rays and are then transmitted through a diffuse transmission plate 8b defining a bottom of the diffuse reflector.
A carrier 10 holds an original picture negative 14 by means of a mask 12. The original picture negative 14 is irradiated with the light rays transmitted through diffuse transmission plate 8b. Then, the light rays are transmitted through an enlarging lens 16. Thus, an image on the original picture negative 14 is projected onto a photographic paper 20 placed on a table 18.
Immediately before the light rays are projected out from diffusion box 8, the light rays reflected on the diffuse reflector, which defines the inner surface of diffusion box 8, tend to be concentrated to a central zone of diffuse transmission plate 8b. As it is well known, the quantity of light transmitted through diffuse transmission plate 8b is relatively large in the central zone and relatively small in the peripheral zone thereof. Consequently, such unevenness in the quantity of light sometimes disadvantageously results in the image projected on photographic paper 20 having a poor quantity of light in its peripheral zone.
One method to avoid this is to configure diffuse transmission plate 8b to be thicker in its central zone than in its peripheral zone. Such configuration will allow the quantity of light transmitted through the central zone to be reduced and thereby allow the diffuse transmission plate to transmit light rays of substantially equalized distribution. This reduces the tendency for the resultant printed picture to be affected by a deficient quantity of light in the peripheral zone and a resulting uneven enlargement due to such unevenness in the light distribution.
Alternatively, diffuse transmission plate 8b may be configured to have a substantially uniform thickness. An attenuating filter 22 having a transmissivity lower in its central zone than in its peripheral zone, as shown by FIG. 6, may be provided at an appropriate location on a section of the optical axis extending from the diffuse transmission plate to the photographic paper 20. In this alternative arrangement, a distribution of the light rays transmitted through said diffuse transmission plate will be uneven but the distribution will be substantially equalized after the light rays have been transmitted through attenuating filter 22.
These techniques well known in the art, as described above, satisfactory provide that the quantity of light projected through the image on the original picture negative and onto the photographic paper 20 can be substantially equalized and further that the picture to be printed out can be protected from any adverse effect resulting from a deficient quantity of light in the peripheral zone.
However, diffuse transmission plate 8b of the above-mentioned particular configuration is required to attenuate the portion of the image at its central zone, which must start out relatively high in intensity, in order to equalize the overall light density of the image with which the photographic paper 20 is irradiated. Accordingly, the overall light density of the image can be equalized but on the basis of the typically low light density at the image peripheral zone. In other words, the quantity of light emitted from the source lamp 2 will be insufficiently utilized and the light that is attenuated will be wasted.
While the rated capacity of the source lamp 2 may be increased to increase the light density of the image, this will make both the light source 1 and the head 6 undesirably bulky and increase power consumption, which is an energy cost.
To change the size of the original picture negative used with the enlarger, carrier 10 is drawn out, original picture negative 14 and mask 12 are exchanged with new ones, and carrier 10 is reinserted. In addition, a head cover 6a is removed and diffusion box 8 is exchanged with one having a size corresponding to that of the new original picture negative 14. Furthermore, the density of light reaching photographic paper 20 depends on the size of the original picture negative 14. Therefore, the density of light with which the original picture negative is irradiated must also be changed by exchange of the diffusion box 8 to maintain the density of light available for irradiation of photographic paper 20 substantially at a constant level.
Such intricate operation of changing the size of the diffusion box has prevented the photographic enlarging operation from being rapidly performed. The conventional arrangement has required also that a plurality of diffusing boxes 8 be used according to the number of sizes of original picture negatives that are accommodated. This adds to the cost of the apparatus.